The contribution of Africa to global greenhouse gas emissions is among the least important, yet Africa’s “key development sectors have already experienced widespread losses and damages attributable to anthropogenic climate change, including biodiversity loss, water shortages, reduced food production, loss of lives and reduced economic growth” (IPCC, 2022). Consequently, a prioritized task for Africa is to improve climate resilience in order to achieve sustainable and equitable development and to guarantee the quality of life for its population. In that context, in January 2021 the International Space Science Institute (ISSI, Bern) organized a workshop on “Global Change in Africa”. The main objective of the workshop was to investigate the benefits of using Earth Observation (EO) data to monitor global environmental changes due to natural phenomena and anthropogenic forcing factors over the African continent and to highlight a number of applications of high societal relevance. Another objective was to discuss the opportunities for collaborations between the international transdisciplinary scientific community and local research institutes as well as with African national and intergovernmental agencies. The workshop, in hybrid form due to the COVID-19 epidemic, gathered 31 participants from 11 different countries, including 6 participants from Africa.

The oral presentations of the workshop covered the various domains of EO for monitoring and understanding global changes in Africa, including water resources, floods and the African monsoon, desertification and droughts in the Sahel, land-use and land-cover change, deforestation and relations with agriculture, exploitation of mineral resources and coastal zone changes. A large variety of remote sensing data and tools, including recent developments in artificial intelligence such as machine learning techniques, is publicly accessible and can indeed help in addressing these topics. A number of data sets were particularly highlighted during the workshop by the different authors, who recognized their adequacies (but also some limitations) to contribute to climate resilience in Africa, including multi-mission satellite altimetry studies such as the Surface Water and Ocean Topography (SWOT, launched on 17 December 2022), Soil Moisture and Ocean Salinity (SMOS), as well as Gravity Recovery and Climate Experiment (GRACE) space gravimetry, and radar and optical imagery from the Sentinel satellites of the Copernicus Programme of the European Union. Limitations and opportunities for future research were discussed in the light of the future missions of the Earth Explorer programme of the European Space Agency (ESA). These images, products and services may be used to document the historical and recent changes over the continent, to understand the respective influence of global or local anthropic activities, and also to address the efficiency of measures and public policies to protect the African populations and adapt human societies to these changes. The use of EO being below its full potential on the continent, a related objective of the workshop was to better understand how EO science, products and applications can better serve the needs of the African population to mitigate the societal impacts of such environmental changes. The presented analyses aim at identifying knowledge gaps and solutions, and recommendations to enhance the uptake of EO products and services in Africa by the stakeholders at the governmental level, as well as by local users, including the development of a private sector.

In each domain of applications, the state-of-the-art information was reviewed, and gaps in knowledge and in observational systems have been identified. The articles of this special issue will provide emerging or confirmed remote sensing academics in Africa entry points into the vast literature of EO applications and capabilities. Existing projects dedicated to global changes in Africa are discussed and evaluated, for example, the TIGER initiative developed by ESA to assist African countries to overcome problems faced in the collection, analysis and use of space-based water data. The present Special Issue consists of a collection of eight overview articles summarizing the main outcomes of the workshop and associated recommendations. General ideas and recommendations related to the uptake of EO products and services in Africa, relevant to all applications, are presented in a first paper, by Speranza et al. (2023), entitled Enhancing the Uptake of Earth Observation Products and Services in Africa Through a Multi-level Transdisciplinary Approach. The following papers are related to the various specific application domains of EO, including water resources and management extreme events (floods or desertification), deforestation and changes of land use, in relation to the exploitation of mineral resources since the gold rush in West Africa, and coastal zone changes.

The next three papers focus on water resources in Africa, including surface waters and groundwater reservoirs. The article from Papa et al. (2023a, b), Water Resources in Africa under Global Change: Monitoring Surface Waters from Space, highlights the cost-effective means provided by EO for monitoring the water cycle over the African continent. The review emphasizes that, despite its importance for the African population, surface water storage in lakes, reservoirs, rivers and floodplains and its variations and changes still remain widely unknown in many parts of Africa. This article highlights how satellite data can be used to monitor these areas or give access to new quantities, such as the inundated area, which are almost impossible to derive from the ground. The article also emphasizes the strong need for a better monitoring of water quality and shows how space-based observations may be used to monitor the suspended matter in lakes and rivers. In the context of upcoming satellite missions (including the recently launched SWOT mission), remote sensing will ensure the continuity of observations and again be a game changer to develop comprehensive observing systems to monitor Africa’s land water and manage its water resources.

In a paper entitled Water resources in Africa: the role of the EO data and hydrodynamic modeling to derive river discharge, Tarpanelli et al. (2023) recall that the number of gauging stations has decreased worldwide and the situation is particularly serious in African countries that suffer more than others from discontinuous and incomplete monitoring. The authors review the methods, including recent developments in the domain of artificial intelligence, for hydrological and hydraulic modeling to estimate river discharge using satellite data, specifically radar altimetry and optical observations. These methods can be used to complement the need for adequate and reliable monitoring of river discharge, especially in data-poor regions, or to monitor the impacts of extreme events, which may become more frequent as a consequence of climate change. They also discuss their role in monitoring climate changes. Emphasis is placed on their relevance for African basins where in situ hydrological stations are very sparse.

The article entitled The Role of Space-based Observations for Groundwater Resource Monitoring over Africa by Springer et al. (2023) highlights the specificities of the ground water resources of the African continent and their vulnerabilities to climate change and summarizes the strengths and weaknesses of satellite remote sensing techniques for studying groundwater storage. This article provides a thorough review of the literature dedicated to the use of satellite observations for groundwater research. It also proposes new concepts to combine satellite observations with numerical models and in situ observations to quantify current groundwater resources and their changes in the different climatic regions of Africa. These new concepts are presented together with a discussion of possible climatic and anthropogenic drivers of the observed changes. Finally, it identifies gaps in knowledge and possible future research directions to value the use of satellite data for groundwater monitoring and water resources management at the continental scale.

The article entitled Hydrometeorological Extreme Events in West Africa: Droughts, by Dibi-Anoh et al. (2023), reviews weather and climate extreme events that affect vast areas of the African continent and discusses the impacts of rainfall variability on agriculture and water resources. The paper focuses on drought events and shows how space data can provide useful information on droughts in West Africa. Satellite-based rainfall and evapotranspiration data analyzed from 1970 to 2013 are shown to be very valuable indicators of risks of water resource scarcity in the hydro-system of the Bandama river in Ivory Coast, which is also currently affected by the expansion of artisanal mining activities (increased use of water and risks of pollution).

Gosset et al. (2023) also discuss extreme meteorological events and, in particular, floods, in a paper entitled Hydrometeorological Extreme Events in Africa : The Role of Satellite Observations for Monitoring Pluvial and Fluvial Flood Risk. They review the state of the art in using space observations for analyzing extreme rainfall and flood events in Africa. Floods occur across many spatial and temporal scales, from very localized flash flood events in an urban context to the slow propagation of discharge peaks in large rivers. They show how satellite data can help to understand the genesis and impacts of flood events, monitor their evolution, and better constrain forecast models, thereby improving early warning and population protection. The paper proposes an analysis of major flood events that occurred in Niger, Mozambique, Central African Republic and Ivory Coast, using satellite information.

Then, the article written by Ngom et al. (2023) addresses the issue of mineral resources exploitation, in particular the non-formal and poorly regulated small-scale and artisanal exploitation of gold, and their impacts on the environment. The paper, entitled Artisanal Exploitation of Mineral Resources: Remote Sensing Observations of Environmental Consequences, Social and Ethical Aspects, discusses how remote sensing techniques should be used in a reflexive manner that accounts for social, ethical and political implications of mining governance informed by Earth observations from space. The value of remote sensing techniques is presented to fill the current knowledge gap on the impacts of the recent expansion of artisanal mining in Africa, and associated problems such as the detection and monitoring of the expansion of illegal sites, the evaluation of the degradation of soils and waters, and deforestation. This article focuses on the advantage of the Sentinel 2 time series and their high frequency of acquisition for the observation of the Earth’s tropical climate which is often impeded by frequent cloud coverage. It also highlights the value of the recent development in artificial intelligence for the challenging identification of artisanal mining sites from space. The article indicates the limitations of remote sensing techniques, which are blind to certain aspects of the social impact of artisanal mining and the need to use these techniques in an interdisciplinary approach involving geographers and geoscientists, anthropologists, economists, and political scientists.

The article entitled Coastal Zone Changes in West Africa: Challenges and Opportunities for Satellite Earth Observations by Almar et al. (2023) discusses the vulnerability of the West African coastal population and ecosystems as a result of increasing hazards due to natural phenomena, climate change and direct human activities. Understanding coastal changes has been limited by an incomplete knowledge of coastal processes and the difficulty of obtaining detailed in situ data. Recent advances in satellite techniques have made it possible to obtain rich coastal data sets that provide a solid foundation for improving climate change adaptation strategies for humanity and for increasing the resilience of ecosystems for sustainable development. The authors review the West African coastal layout and current socio-environmental challenges together with the key parameters that can be monitored from space, as well as coastal management programs that rely on satellite techniques. They identify the social, technical and scientific problems and difficulties that hinder the interest of coastal practitioners and decision-makers in the use of satellite data. They finally provide a roadmap for precisely responding to these difficulties and for better supporting future coastal zone management in West Africa.

The organizers of this Workshop are most grateful to ISSI for hosting and for the sponsorship of this event, to the reviewers for their hard work, which led to improvements in the quality of the published articles, to the Editor in Chief, Professor Michael Rycroft, for his advice, and to the staff of Springer Nature for publishing this Special Issue efficiently.